Flue gas reheat apparatus

Abstract

Flue gas is passed through a first heat exchanger, a wet scrubber, and a second heat exchanger. The first heat exchanger supplies heated liquid to the second heat exchanger to reheat the flue gas. The first heat exchanger comprises, and the second heat exchanger ideally comprises, a plurality of fluoroplastic-covered metal tubes extending through a fluoroplastic-lined gas passage.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows: 
     
       1. In flue gas treatment apparatus which includes a first heat exchanger connected to receive flue gas and transfer heat from said flue gas to a liquid, a wet scrubber connected to receive flue gas from said first heat exchanger and to mix a scrubbing liquid with said flue gas to scrub the same, and a second heat exchanger connected to receive scrubbed flue gas from said scrubber and to raise the temperature of said scrubbed flue gas, and means to circulate said liquid between said first and second heat exchangers, wherein said first heat exchanger comprises housing means defining a gas passage, and a plurality of tubes extending through said gas passage, said tubes being covered with corrosion protection coverings and said liquid being connected to pass through said tubes, the heat transfer surface areas of said heat exchangers, the circulation of said liquid between said heat exchangers, and the temperatures of flue gas entering said first heat exchanger and exiting from said second heat exchanger being so related that the temperature of that liquid received by said first heat exchanger is below the acid dewpoint of flue gas entering said first heat exchanger, whereby acid is formed in said first heat exchanger. 
     
     
       2. Apparatus according to claim 1 wherein said corrosion protection coverings comprise a fluoroplastic. 
     
     
       3. Apparatus according to claim 1 wherein said first heat exchanger comprises a pair of spread apart tube sheets forming portions of said housing means, the interior surface of each of said tube sheets being covered with a corrosion protection covering, each of said tubes extending through a respective pair of holes in said tube sheets and being gripped by said coverings on said tube sheets. 
     
     
       4. Apparatus according to claim 2 wherein said coverings have a thickness in the range of 2-30 mils. 
     
     
       5. Apparatus according to claim 1 which includes a third heat exchanger connected to supply said flue gas to said first heat exchanger, said third heat exchanger being operative to cool said flue gas to a temperature which is in between a material deformation temperature of said corrosion protection coverings and the acid dewpoint of the flue gas supplied to said first heat exchanger.